I would like to upgrade my Canon 5D to a 5D Mark III but I'm also on a budget. I got interesting offers from photographers upgrading to the 5D Mark IV, the problem is the shutter counts are well above 300K actuations.
I am afraid there might be electronics burnout problems which would cost far more than a simple shutter replacement.
Is it advisable to buy a camera with such a huge shutter count?
The Canon rating for Mean Actuations Before Failure of its 5DMkIII is 150,000 actuations.
Now, this doesn't mean that a shutter will "on average" live to only 150,000 actuations. The mean means that as many shutters that Canon produces will fail before 150,000 actuations as fail after 150,000. These numbers are generally lower than what an individual should expect, however, because there is a spike in shutter failures in the low-thousands (due to clear manufacturing defects), and then a fairly long narrow tail beyond that. So, if the shutter has outlasted the initial manufacturer's warranty, it is likely to get much more than 150,000 actuations.
Looking at actual self-reported values at http://www.olegkikin.com/shutterlife/canon_eos5dmkii.htm - sorry, nothing for the Mark III, but the Mark II had the same rated MTBF of 150,000 actuations - we see a 66% chance of a shutter living beyond 1 million actuations (!) Of course, this is all self-reported, and those who get up to 1M actuations are likely treating their cameras differently than those who just hit 100k actuations nine years after release. But it gives you an idea of what the possibilities are.
Of course, it is all a gamble. If you are getting a camera at a good deal, and are able to put $200 in a savings account for if/when the shutter fails, you'll be in good shape.
Beyond the shutter, everything else you should be able to see with a bit of a "test drive". This is why I'd advise buying locally rather than over ebay or similar. Make sure the buttons are still firm and function. We focus primarily on the shutter as that is the most likely place for failure you can't see just by holding the camera and taking some pictures.
Also, if you want a little more assurance, go with an official refurbished camera from Canon or an authorized reseller/repair outfit. For instance https://shop.usa.canon.com/shop/en/catalog/eos-5d-mark-iii-body-refurbished has the 5DmkIII at $1999 right now.
Obligatory anecdote: my 40D shutter died at just a hair over 150,000 actuations in 2012. It was disappointing, but still about 50% beyond Canon's MTBF. Fixing the shutter by that point didn't make sense so I just saved up to buy a new camera and limped along with my wife's T1i (which, in the intervening years, has packed on more actuations than the 40D had!) Finally got around to replacing the 40D with an 80D a few weeks ago.
